The complexes trans-Cp*W(NO)(CH2CMe3)-(H)(L) (Cp* = eta(5)-C5Me5) result from the treatment of Cp*W(NO)(CH2CMe3)(2) in n -pentane with H-2 (similar to 1 atm) in the presence of a Lewis base, L. The designation of a particular geometrical isomer as cis or trans indicates the relative positions of the alkyl and hydrido ligands in the base of a four -legged piano -stool molecular structure. The thermal behavior of these complexes is markedly dependent on the nature of L. Some of them can be isolated at ambient temperatures [e.g., L = P(OMe)(3), P(OPh)(3), or P-(OCH2)(3)CMe]. Others undergo reductive elimination of CMe4 via trans to cis isomerization to generate the 16e reactive intermediates Cp*W(NO)(L). These intermediates can intramolecularly activate a C-H bond of L to form 18e cis complexes that may convert to the thermodynamically more stable trans isomers [e.g., Cp*W(NO),(PPh3) initially forms cis-Cp*W(NO)(H)(k(2)-PPh2C6H4) that upon being warmed in n-pentane at 80 degrees C isomerizes to trans-Cp*W(NO)(H)(k(2)-PPh2C6H4)]. Alternatively, the Cp*W(NO)(L) intermediates can, effect the intermolecular activation of a substrate R-H to form trans-Cp*W(NO)(R)(H)(L) complexes [e.g., L = P(OMe)(3) or P(OCH2)(3)CMe; R-H = C6H6 or Me4Si] probably* via their cis isomers. These latter activations are also accompanied by the formation of some Cp*W(NO)(L)(2) disproportionation products. An added complication in the L = P(OMe)(3) system is that thertholysis of trans-Cp*W(NO)(CH2CMe3)(H)(P(OMe)(3)) results in it undergoing an Arbuzov-like rearrangement and being converted mainly into [Cp*W(NO)(Me)(PO(OMe)(2))](2), which exists as a mixture of two isomers. All new complexes have been characterized by conventional and spectroscopic methods, and the solid-state molecular structures of most of them have been established by single-crystal X-ray crystallographic analyses.